1. Field of Invention
The present invention relates to a method for microencapsulating agriculturally active substances and, more specifically, to the production of microencapsulated chemical and/or biological actives having improved resistance to environmental degradation, especially that caused by exposure to ultra-violet (UV) light. Said actives can be any UV sensitive synthetic or natural or biologically derived pesticide.
The use of microencapsulation as a means of controlling the release of actives, of improving handling via reduced toxicity and of improving environmental stability has been documented. Without such protection, the effectiveness of such actives can be drastically reduced by numerous factors including volatilization and degradation caused by exposure to ultra-violet light. By use of the process described herein, the resistance of UV sensitive chemical and/or biological actives to such losses can be greatly reduced.
2. Prior Art
A number of microencapsulation systems have been proposed for prodding protection of agriculturally active substances.
One method suggested in U.S. Pat. No. 3,839,561 utilizes diisophorone derivatives to protect active cyclopropane carboxylic acid compounds from ultra-violet induced degradation. Similarly, U.S. Pat. No. 4,094,969 describes the use of a sulfonated copolymer of catechin and leucocyanidin as a UV stabilizer. In both cases, however, the formulations suggested do not maintain the sunscreen and active in close enough contact to be effective.
In U.S. Pat. No. 3,242,051, a method for coating materials by phase separation is described. Gelatin and various carboxylated polymers such as gum acacia and ethyl cellulose are used to form the coating. The use of a similar ethylcellulose/gelatin system is described by Ignoffo and Batzer in "Microencapsulation and Ultraviolet Protectants to Increase Sunlight Stability of an Insect Virus", J. of Econ. Entomology, Vol. 64, pp. 850-853 (1966), and the use of a chlorophyll green/gelatin system is described in U.S. Pat. No. 2,090,109. In these cases, however, the materials have less than desirable environmental stability. Another disadvantage of these polymers is that they are not always capable of keeping the sunscreening agent within the capsule wall.
Encapsulation of actives by interfacial polycondensation is described in U.S. Pat. Nos. 4,280,833 and 4,417,916. The actives thus formed have a skin or thin wall of polyurea which improves release characteristics and environmental stability. In the process, lignin sulfonate is used as an emulsifier.
The use of lignin in controlled release of actives is also known in prior art. The preparation of controlled release composites of lignin and biologically active materials is described in U.S. Pat. No. 3,929,453 (Re. 29,238). The composites described are obtained by coprecipitation-inclusion from an aqueous alkaline lignin solution, or by the elimination of a common solvent from a lignin-biologically active organic agent mixture. Preparation of reversibly swellable lignin gels is described in U.S. Pat. Nos. 4, 184,866 and 4,244,729. The described gels are formed by crosslinking lignin with epichlorohydrin and are able to sustain the release of water-soluble and water-insoluble pesticides. The use of other crosslinking agents such as formaldehyde and glutaric dialdehyde is described in a related U.S. Pat. No. 4,244,728. The use of said gels for UV protection, however, is not disclosed in any of these patents.
The use of sunscreen agents in combination with encapsulation is described in U.S. Pat. No. 4,844,896. Suggested sunscreen agents include methyl orange, malachite green, methyl green and other colored dyes, and suggested encapsulating agents include Eudragit L, Eudragit S, polyacrylic acid and other polyacrylates. It is claimed that such systems keep the sunscreen agent within the capsule. Incorporation of the sunscreen into the capsule wall is not disclosed, however, and the problem of sunscreen catalyzed degradation is not addressed.
The use of lignin or lignin in combination with polyacrylate materials as an encapsulating agent is described in International Application No. PCT/US92/03727. While lignin is disclosed as a sunscreen in this application, the procedures used to make capsules are complex and require a number of different chemicals.
The objective of this invention, on the other hand, is to incorporate ultra-violet sunscreens, and more specifically sulfonated lignins, sulfonated lignites, naphthalene sulfonates and other related compounds, directly into the wall of the capsule. Chemical bonds keep the sunscreen agents from diffusing out of the capsule where they are ineffective. A further objective of incorporation of the sunscreen into the capsule wall is to minimize sunscreen catalyzed degradation of sensitive actives.
Still another objective of the invention is to minimize the number of ingredients needed in the encapsulation procedure, thereby simplifying the overall process.
Other objectives and advantages of the invention will become evident on reading the following detailed description.